Are you referring to the brains ability to develop/evolve contol over extra appendages, or the evolution of the mind in general?
If it is the first, then I would say that as long as there are motor control and nerve connections, then the brain adapts/evolves to control the appendage just like a newborn learns to control any of it's normal appendages.
In cases of severe brain injury, sometimes when portions of the brain are removed, the brain has the ability to find new pathways and relearn lost skills.
There are certain autonomic functions that are present from inception/birth (ie breathing, heart beat, etc...) animals, like a newborn colt, have the imprinted, instinctive ability to walk and nurse.
Regarding the evolution of the brain...one circuit at a time, simple to complex, is my suspicion (based on my limited knowledge).
Remember that I am a Theistic Evolutionist, so I believe that God is in control of his ultimate plan for any evolutionary development.
Before I comment I would like to have some information from you so that I know what I am dealing with. I never really understood the arguments of theistic evolutionists until coming to this site. Like you I believe that God could use evolution to bring all things into existence under the all things are possible with God scripture. I also believe that God could create by divine fiat instantaneously as indicated by JesusÃ¢â‚¬â„¢ first public miracle. So my question to you is does God have a choice over the way He chose? Because the alternative to me means you are telling Him how He had to do it,
I have never read any posts where you argue that God could have created man as a miracle like Jesus did when He turned water into wine.
Gen 2:7 And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
So do you think God had a choice in the matter? Did you ask God which method He chose?